Telephone system



March 10, 1942. H. NYQUIST TELEPHONE SYSTEM I Filed May 31, 1940 l3Sheets-Sheet 1 S 9 u k t 3 Q k5 K5 6 u g I P. I

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TELEPHONE SYSTEM Filed May 51, 1940 13 Sheets-Sheet 2 /NVENTOR H. N YQU/ST Y A TJ'ORNE Y March 10, 1942. H. NYQUIST TELEPHONE SYSTEM 13Sheets-Sheet 3 Filed May 31, 1940 INVENTOR H. N YQ 0/5 T Cw-q A 7'TORNEY Ma rh 10, 1942.

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Fild May 51, 1940 13 Sheets-Sheet 5 EHIU INVENTOR By H. N YOU/ST wwwqfwATTORNEY March 10, 1942. I H. NYQUIST 2,275,459

TELEPHONE SYSTEM Filed 'May 31, 1940 13 Sheets-Sheet 6 INVENT'OR B y H.N YQU/S T ATTORNEY March 10, 19.42. H. NYQUIST 2,275,459

TELEPHONE SYSTEM Filed May 31, 1940 13 Sheets-Sheet 7 INVENTOR H.NVQU/$TBKWWWWW A TTORNE Y Marh 10, 1942. H, NY ULST 2,275,459.

TELEPHONE SYSTEM Filed May 31, 1940 13 Sheets-Sheet 8 TRA N: L A TINGMECHANISM //v VENTOR H NVQU/ST WWW U .ATTORNE Y March 10, 1942. NYQUlST7 2,275,459

TELEPHONE SYSTEM File d May 31, 1940 13 Sheets-Sheet mm LLL g L m wggsum V 1 HNYQU/ST B V wmvgmw @H a A TTORNE V March 10, 1942.

H. NYQUIST TELEPHONE SYSTEM Filed May 31, 1940 13 Sheets-Sheet l0M/vE/vToR By H N Y6? U/ST ATTORNEY 253mm .89 Q9 39 bQQ March 10, 1942.H. NYQUIST TELEPHONE SYSTEM 13 Sheets-Sheet ll Filed May 31, 1940INVENTOR By mvrpu/sr mwqonmm v5 .rH I. v9

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FIG /2 TERM/NAT/NG TOLL OFFICE Filed May 51, 1940 H. NYQUIST TELEPHONESYSTEM 13 Sheets-Sheet 12 MARKER lNl/ENTOR H. NVQU/ST A T TORNEV FiledMay 31, 1940 13 Sheets-Sheet l3 SEA/DER B V H NYQU/ST ATTORNEY INl/ENTOR Patented Mar. 10, 1942 TELEPHONE SYSTEM Harry Nyquist, Millburn,N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application May 31, 1940, SerialNo. 338,001

22 Claims.

This invention relates to telephone systems and particularly to systemsin which long-distance connections are established automatically.

The objects of the invention are to enablea more efficient use of thedirect and alternate routes available in the automatic establishment ofconnections between remote oiiices in large toll areas; to increase theflexibility of switching systems in the extension of such connections;to make provision for automatically varying the routes available inaccordance with traffic conditions existing in the area involved; toincrease the speed and reliability with which call designations aretransmitted over long distances to control switching operations; toutilize the call designation signals for controlling the establishmentof long-distance connections and also for determining the transmissioncharacteristics of said connections; and in other respects to obtainimprovements in systems of this character.

Systems have been proposed heretofore for the establishment of tollconnections by automatic switches controlled by subscribers or operatorsdials. Also systems have been devised in which calls are extended fromany given point over:

direct trunks as a preferred choice and over alternate-route trunks as asecondary choice in case the direct trunks are not available. However,none of these prior plans makes it possible to obtain the most efficientuse of the many toll trunks that interconnect the numerous toll officesin a country-wide system.

According to a feature of the present invention, advantages are realizedover these prior arrangements by means of a system in which longdistanceconnections are extended automatically over trunk lines interconnectingsuccessive offices; in which each office makes a registration,

as the call progresses, of the busy and idle condition of all routestested; and in which the registration thus established in a given omce,which has already extended the call to an office beyond, causes theswitching mechanism in said given oflice to reroute the call over anuntried alternate path in the event the office beyond fails because allroutes available to it are found busy or out of second trial over a newroute after its first and initially successful trial over the preferredroute has met with failure at some point beyond.

Another feature is a system in which the routing registrationestablished in any particular office causes the switches in that ofiiceto release the connection, originally extended therefrom, when theregistration indicates that all available routes are busy, and toreroute the connection over an alternate route from said particularoffice to another office beyond,and in which the routing registration isthen transferred from said particular office to said office beyond.Since this registration shows the condition of the routes testedfollowing the first attempt to complete the connection from saidparticular office, and since some of these routes are normally availablefor completing the connection from said office be yond, the transferredregistration serves the useful purpose of indicating to the controlmechanism in said ofiicebeyond which routes are busy, thus obviating afutile attempt to extend the connection over these routes and directingthe trials to other routes.

Another feature of the invention is a system in which the toll oflicesare equipped with senders and markers for controlling the selectiveswitches therein to extend the connection from one oifice to another, inwhich the code designation of the called toll omce is transferred fromone sender to the next as the call progresses, in which the trunknetwork available to one office may differ from that available to theuse of other offices, and in which the marker in any particular ofilceanalyzes the code received and determines the trunk pattern available toit for the extension of the call.

Another feature of the invention is a system in which the codedesignation of the called toll of fice is utilized in the originatingtoll ofiice to determine whether certain transmission equipment, such asecho suppressors, shall be included in the connection and to determinethe intermediate office at which this equipment is to be connected. Whenthe connection has been extended from the originating office through theintermediate offices to the terminating ofiice, a signal is transmittedover the connection to identify the particular intermediate ofiice atwhich the echo suppressor is required. Signals are also transmittedgiving the identification of the calling ofhce and the route over whichthe connection was extended therefrom to the intermediate echosuppressor ofllce. This information, together with similar informationconcern ing the called office and the route thereto already recorded inthe echo suppressor office makes .it possible to adjust the delay valuesof the suppressor to give the best transmission characteristics. y i

Another feature of the invention is a system of the kind above describedin which the designation of the called office and the supervisory andother signals are transmitted over the extended connection by means ofcarrier frequency channels.

Another feature of the invention is a system in which the signalreceiving mechanism in the originating office is tuned to a narrow bandfor receiving specific signals during the time the connection isestablished and is automatically tuned to a wide band for receiving thespeech signals of the operator or the called subscriber at the distantend. These speech signals serve apparatus of a toll exchange systemembodying the features of this invention;

Fig. 2 shows acalling local oifice located inthe area served-by one ofthe toll offices;

. Fig. 3'shows the controlling equipment in the local o ffice, includingsenders and markers for controlling the operation of the automaticswitches illustrated in Fig. 2;

Fig. 4 illustrates the originating toll omce serving the local ofiice ofFig. 2 and shows automatic switches over which calls from the localoffice are extended to distant toll offices. This figure alsoillustrates two of these distant intermediate toll oflices; I

Figs. 5, 6 and 7 disclose one of the common register senders in theoriginating toll oflice; of Fig. 4;

Fig. 8 shows one of the markers in the origi" nati'ng toll office whichcooperates with the register sender to control the operation of theautomatic switches;

Fig. 9 illustrates a third distant or intermediate toll office and showsthe automatic switches therein for extending incoming calls to stillmore distant toll offices;

Fig. 10 illustrates one of the common register senders in the thirdintermediate toll oflice;

Fig. 11 illustrates one of the switch controlling markers and also atiming mechanism located in said third toll office;

Fig. 12 illustrates a fourth intermediate toll office and also shows afifth toll office, which is here illustrated as a terminating ofiice;and

Fig. 13 illustrates a called local office in the area served by theterminating toll office.

Since each office in the system is interconnected with other officesover a plurality of different trunk routes, it is possible, by providingthe necessary switching and controlling facilities, to make the mosteffective and efficient use of the trunking network in the extension ofa toll call originating in any one of the toll offices and destined forcompletion through any other toll office. To this end each toll officewill have a particular route over which it prefers to extend its callsto another office in the system, and this preferred routing may bechanged from time to time by simple Wiring alterations made in the Thepresent invention is particularly applicable controlling equipment.Likewise, each ofiice in the system will have a number of alternateroutes to any other particular office, and these will be triedsuccessively in a certain fixed order until an available one is found oruntil it is determined that all routes are unavailable.

For example, the toll office 400 may prefer to use trunks dill, 499, 4H,9H, and 9M for extending its calls to the office IZM. If trunk M11 isbusy, the office Mill may then prefer to extend these calls by way oftrunks M6, 432, 4H, 9H and 914. But if trunk 432 is busy, it may thenprefer to extend the call by way of trunks MB, $31, 425, 9H and 9M. Andin similar manner other patterns may be used as subsequent choices inthe extension of the call from office 4M] to office i280. Similarly,each office in the system has a preferred route over theseinterconnecting trunks to each other office and a plurality of alternatechoices.

A call may progress successfully over several interconnecting trunks andthen find itself blocked because all routes ahead are busy or otherwiseunavailable. This does not mean, however, that the call must fail,because there still may be several available routes between theoriginating oilice and the called office. For instance, a callfromoffice liili to office [280 may have progressed successfully overtrunks Ml, W9 and MI to the office 980. Office 908, however, finds bothtrunks 9H and 52! busy, but some or all of the trunks 423, 42L 9M, 428and Q29 may be idle at this time; therefore, the call should not bepermitted .to fail notwithstanding the fact that office 9% is powerlessto reach these idle trunks with its own switching equipment. To make useof these idle trunks rather than allowing the call to fail, it is onlynecessary to provide some means for releasing the partial- 1y completedconnection back to the preceding ofilce 28 and to provide means inoffice 420 for rerouting the call over its alternate route 423 to theofiice Add. Thereupon the ofiice 440 is free to further extend the callover trunks 421 and 9M if both are idle or, alternately, over trunks $28and 429 to the called ofiice I200. Should the ofiice Mil on its secondattempt find the alternate route trunk 4323 busy the connection isreleased back to the next preceding office M0. In like manner the officem reroutes the call over its alternate route trunk 424 to the office43%, assuming this trunk to be idle, and office 2-33 proceeds to furtherextend the call over available routes between it and the called officeI200.

This comprehensive method of routing and rerouting a call to obtain thefullest advantage from the trunking system is made possible by providingeach toll oifice with a route registering mechanism. The function of theroute registering mechanism in each toll ofiice is to establish andmaintain a complete registration of all trunk routes beyond that officethat are tested in the process of projecting a connection toward aterminating oflice in the area. Since, therefore, each office throughwhich the connection is extended keeps a registration of every trunkroute tested beyond, it is possible for any particular oflice to releasethe connection forward as soon as it determines that the call has failedto find an idle route and to reroute the call over an alternate trunkroute to an untried office beyond. The routing pattern available to aparticular office will, of course, vary in accordance with the calledoffice in the system. The route recording mechanism, however, isuniversal in this respect and is capable of selecting the proper routepattern as soon as the designation of the called office is received.Hence any ofiice in the system, when called upon to extend a connectiontoward any distant terminating office, is capable of automaticallydetermining a pattern of preferred and alternate routes available forthat particular call and to keep a registration of the condition of eachtrunk tested in the selected pattern. With this information, thecontrolling mechanism in the ofiice is able to determine what routes areavailable, to cause second trials as long as there is hope of extendingthe connection. over the chosen route, to recognize the existence of acomplete failure over the chosen route, and to release an office fromthe connection in favor of a preceding office which may ultimatelysucceed in completing the desired connection.

A general understanding of the equipment used in the system disclosedherein may be had by referring to Figs. 2 to 13, inclusive, of thedrawings. These drawings'illustrate a calling local oflice, anoriginating toll ofi'ice, several intermediate toll offices, aterminating toll office and a called local ofiice. It will be obvious,however, from the foregoing description of Fig. 1 that any number ofintermediate toll offices may be involved.

The calling local office 209, shown in Figs. 2 and 3, may be of anytype. ever, it is an office of the automatic type and is provided withthe usual operators position equipment 220 and with operators cordcircuits 2!! for extending calling lines to the toll office. For thispurpose the operator has access to trunks, such as the trunk 21',terminating in the district selector switch 202. The trunk 20! also hasaccess through a sender link connector 203 to idle register senders, oneof which is disclosed partly in detail in Fig. 3. The register senderwhen associated with the trunk 29! seized by the operator responds tothe operators keyboard and registers the code designation of theterminating toll office and also the code designation of the calledlocal oifice and the number of the wanted line in the called localofiice. Thus the complete information concerning the call is firststored in the sender of the calling local ofiice. Without limiting theinvention in any way it may be assumed that the toll area is of suchmagnitude that five code digits are required to designate any particularcalled toll office and to include such other information as may berequired in the extension of the connection. These five toll code digitsare registered in any conventional manner on registers 3&2, 303, 324,305 and 305 in the sender. The called office code, which may comprisethree digits, is registered on registers 331, 386 and 369, and thenumber of the called line called is registered on the As illustrated,how

numerical registers 3H 3! I, 312 and M3. After the designations havebeen registered, the sender seizes an idle marker 3! through a markerconnector 3l5. The toll code digits are then transferred to the marker,and the marker utilizes this information to selectively operate thedistrict and ofiice switches 202 and 204 to seize an idle trunk 205extending to the originating toll office 400. The marker controls thedistrict and office switches in the usual manner by connecting itselfthereto through the frame connectors 206 and 201. The marker alsotranslates the toll code and sends the translated registration back tothe sender where it is registered on a set of transmitting registers3l6.

The local office sender is provided with carrier frequency signalingequipment having a substantial number of frequency channels by means ofwhich information is transmitted from the sender to senders in thedistant toll offices and by means of which supervisory and otherinformation is received from the distant offices. The variousdesignation characters and supervisory signals may each be representedby a single frequency or by a code of frequencies simultaneously sentover the signaling circuit. To this end the transmitting signalingequipment in the local ofiice sender includes a source of alternatingcurrent 3", a harmonic generator 3|8, channel filters 319, 32!], 32!,etc., detector amplifiers 322, 323, 324, etc. For example, thesetransmitting signal channels are used to transmit the translated tollcode from the calling office to the toll office, to transmit supervisoryinformation when the connection has finally been extended to theterminating toll office, and to transmit the called ofiice code and linenumber to said terminating oflice. The signal receiving mechanism in thesender comprises a plurality of frequency selecting filters and detectoramplifiers, including filters 325, 326, 321, 328, 341, and detectoramplifiers 329, 330, 33L 35$ and associated circuit controlling relays.

The trunk 265 extending from the local office enters the toll oflice 400and appears in the automatic switch M2. Since the trunk 205 may be atwo-way circuit, the function of the switch M2 is to extend this trunkto an idle junctor 4M on an inward call and to seize the trunk 205 on anoutward call for the purpose of extending the desired connection fromthe toll oflice to the local ofiice. The junctor or trunk 40! appears inthe district selector switch 492 and also has access, through a senderlink connector 433, to register senders, one of which is shown in Figs.5, 6 and '7.

The register sender in the toll office 400 includes toll designationregisters 53L 532, 503, 504 and 535 for registering the designation of aterminating toll omce. These registers are set in response to carriercurrent signals incoming to the signal receiving mechanism in the senderfrom a distant local or toll ofiice. depending upon the origin of thecall. The signal receiving mechanism 5% includes a plurality of channelfilters and detector amplifiers. The sender also includes signaltransmitting mechanism comprising generators 59'! and 598, harmonicgenerators M2 and 559 and associated channel filters and amplifierdetectors and switching relays for transmitting designation routing andsupervisory signals over the extended connection, both in the directionof the originating ofiice and in the direction of the terminatingoffice.

The toll office sender also includes the routing terminating ofiice.

';mechanismshown in Figs. 6 .and 7. Thismechanism comprises :a plurality.of relays which :are operated, when thecall is first received, inaccordance with the designation 'of the terminating toll office todetermine the pattern of the trunk network beyond that will be used "inextending the call to the terminating office. This pattern:determinaticnis effected by the switch :controlling marker 86!;which isseized by the register sender through a marker connector 382 andwhichreceives on its registers 803, 3%, '885, 836 and 81 the'toll designationof the terminating ofiice. This code designation is translated andanalyzed by the marker and utilized to operate the necessary relays inthe routing mechanism to determine the available route :network for theextension of the call.

The marker 89!, having received the toll code and'having translated it,proceeds to control the operation or" the selector switches M32 and Mil, through the frame connectors M35 and 486, to

extend the connection over the preferred or direct route trunk AMoutgoing to the next toll office MU beyond. If the trunk M1! is idle andthe call is successfully extended over this route, a signal istransmitted to the routing mechanism to register the fact that the firsttested link in the network pattern is idle. V

Thereafter the toll offices beyond, which will be described presently,further extend the connection over the preferred routes, if idle, towardthe If the preferred routes are found idle, success signals aretransmitted back 'to the originating ofiice sender, causing the0peration of the relays in the routing mechanism. These-operated relaysregister the fact that the preferred links beyond are idle. On the otherhand, if any one of the preferred links beyond is busy, an alternateroute is attempted, and a failure signal is sent back to the originatingtoll office where it causes the operation of a relay in the routingmechanism to register the busy condition of the tested link. In thissame manner success and failure signals are transmitted back over theconnection each time a route is tested .3

during the progress of the connection toward the terminating oflice, andthe routing mechanism registers these signals and thus establishes acomplete registration of the condition of the tested links or routes inthe routing pattern chosen for the particular call being extended.

To explain more specifically how the marker 'SGI determines the initialsetting of the routing mechanism for the selection of the appropriatepatern, it may be noted that the marker is provided with the usual routerelays, such as the relays 898, 899, 8H], EH9, 820. Generally speaking,there is one of these relays in the marker for each toll codedesignation that may be received on the registers of the marker.However, in some cases remote olfices which are not regional centers maybe represented by a single route relay. The route relay, therefore,represents the terminating toll ofiice, and its contacts may be wired insuch a manner that relays in the routing mechanism are operated todetermine the particular trunk routes available for the completion of acall to that terminating ofiice. By extending the circuits from thecontacts of the route relays through a wiring rack or terminal strip Itype for extending calls in both directions.

route relays may the .made common to .a number of :markers which seizethem for use when required.

'The marker IiIlI, having received and analyzed the toll code, transmitsthis registration, either in its original form or in translated :formaccording to the location of the terminating office, back into thesender where it is registered on the transmitting registers 5m in thesender. When the proper time arrives, this registration in the senderwill'be transferred therefrom .over theiextended connection to the.sender in the succeeding toll ofiice. Where translation of the tollcode is not required, the sender may bearranged to send this code to theoflice beyond under :con-

'trol of the registers von'whichiit is received "from the precedingofiice and without the assistance of the marker.

The toll trunks 481, 489, All interconnecting the successive tolloflices may be of the two-Way At the intermediate oflice 9%, forexample, the automatic switch 9M serves to extend .the trunk MI ineither of two directions, depending upon the direction of the particularca'll'involved. On an inward call from ofiice 420, the trunk MI 'isextended by the switch Bill to the junctor 962 which appears in thecontacts of the district selector switch '9ll3. The junctor 9512 hasaccess through the sender link "connector 934 to're'g'ister senders inthe oiiice 900, one ofwhich is illustrated in Fig. 10.

It will be understood that the register senders in the several tolloffices may be substantially the same, although the sender illustratedin the drawing for the originating toll ofiice 400 shows some parts thatare omitted from the sender in the ofiice 9G0, and the latter senderillustrates some parts that are omitted from the sender of theoriginating oflice. Like the sender in the originating toll office, thesender of the intermediate ofiice 9'00 is provided with registers mm,I002, I903, I064 and I885 for registering the code designation of theterminating toll office. This designation is transferred, as abovementioned, from the sender in the originating toll office and isreceived by the carrier signal receiving mechanism H386 and registeredon the registers IIIBI to I885. The sender in the intermediate oflice isalso equipped with a routing mechanism I6 I1,

similar to the one shown in Figs. 6 and 7.

The intermediate 'toll oflice is also provided with a marker IIBI whichcooperates with the sender through the marker connector H02 and servesto control the operation of the automatic switches 933 and 905 to extendthe connection over a toll trunk "9H to the next succeeding toll In viewof the long distances that may be involved in some toll connectionswhere several trunks are connected in tandem, it is desirable to providecertain of the toll oflices in the area with devices, such as echosuppressors, for improving the transmission characteristics of theselong connections. "It may be assumed that the intermediate toll o'flice960 is equipped with a number of echo suppressors, such as the"suppressor 996. The function of the suppressor is to respondautomatically to speech transmission in either direction and after aninterval of delay to open or disable the transmission circuit in theopposite direction. The purpose of opening the circuit is to prevent anecho reflected from the called end of the line from passing thesuppressor and returning to the talking party. The,

amount of delay should be just long enough to intercept the returningecho. In the present system disclosed herein the inclusion of asuppressor in any particular connection or its omission therefrom isdetermined automatically from the code of the called office, and theinclusion of the suppressor, when required, is effected automatically.Moreover, the delay intervals for transmission in both directions areadjustable automatically in accordance with the transmission distancesbetween the suppressor office and the terminals of the connection. Theselection of a suppressor is effected by transmitting a distinctivesignal from the originating toll office to the'suppressor ofiice. Thissignal is received like the other signals and causes the operation of asuppressor connector switch 908, which merely serves to connect thesuppressor 906 in the talking conductors of the junctor 902. The amountof delay for the transmission circuit extending from the originatingtoll office to the suppressor ofiice is determined by the codedesignation of the originating office and by the particular route thatwas used in extending the connection from the originating office to thesup pressor office. The code designation of the originating office istransmitted therefrom at the proper time to the suppressor office and isregistered on the registers I001, I008, I009, IMO and IBM in the sender.The exact route used in extending the connection from the originatingoffice to the suppressor oiiice is known by the routing mechanism in theoriginating office. Accordingly, this information is transmitted in theform of carrier signals over the extended connection and registered onthe calling route registers IOI2, IOI3, I014, H and IOI6in the sender.The setting of these registers is transferred through a connector I I03to a decoder I I04. The decoder I104 analyzes the calling oince code andthe route information and utilizes this information to set the variablyoperable delay switch 909 in the suppressor 906. Concerning the delayrequired for the transmission line between the suppressor office and theterminating office, it will be noted that the sender in the suppressorofiice already has recorded therein the designation of the calledoffice. Furthermore, when the connection has been fully completed to thecalled oflice the routing mechanism IOI'I has a full registration of theparticular route chosen in extending the call from the suppressor ofiiceto the terminating oflice. Hence the called toll office code and therouting information are similarly transferred to the decoder H04, whichanalyzes this information and proceeds to operate the variablyadjustable delay switch 9I0 in the echo suppressor to determine theamount of delay appropriate for the transmission line between thesuppressor ofiice and the terminating toll office.

The toll trunk 9| I extends to the next toll office 9I0, from whence theconnection may be further extended over trunk GM to the office I200,which is assumed to be the terminating toll office. At office I200 thetrunk 9M, which also may be of the two-way type, appears in an automaticswitch I20I. The switch I20I extends the connection to a junctor I202terminating in the district selector switch I203. The junctor I202 alsohas access through the sender connector I204 to the sender I205, whichis similar to the senders in the other toll ofiices. The sender I205 hasaccess to the marker I205 through the marker connector I20! and themarker, in cooperation with the sender, controls the switches I203 andI208 to extend the connection over a trunk I200 to the called localoffice I300, illustratedin Fig. 13.

The incoming trunk I209 appears in the incoming selector switch I30l inthe local office, and the selector I30I, in conjunction with the finalswitch I302, serves to complete the connection to the called subscribersline I303. The switches I30I and I302 are controlled by the sender I304and marker I305. Since the invention is not particularly concerned withthe types of automatic switches that are used in extending theconnections, nor with manyof the details of the controlling mechanismswhich determine the selective operation of the switches, the disclosurehas been simplifled to a large extent to faciiltate a clearerunderstanding of the invention by omitting many of the unessentialcircuit details.

It is assumed, however, that the local and toll oflices in the systemherein disclosed are equipped with automatic switches of the well-knowncrossbar type, although these offices might be provided with other kindsof switches, such as step- .by-step switches, panel switches, or relayswitches. The register senders and markers provided in each office forcontrolling the cross-bar switches therein are, in general, similar tothose disclosed in numerous prior art patents. Also the severalconnecting devices, such as the sender connectors, the marker connectorsand the frame connectors, may be essentially the same as those alreadydisclosed in the prior art patents. For a more complete disclosure ofthe cross-bar system, of the manner in which the register sendersreceive and register the designations, of the manner in which thesesenders cooperate with the markers, of the manner in which the markerstest the trunk groups, select idle trunks, control the selectiveoperation of the switches to extend the desired connections, of themanner in which the marker supplies the sender with informationconcerning the further extension of the connections, of the manner inwhich the senders transfer information to distant offices and receivesupervisory information therefrom, and of the manner in which theestablished connections are held during conversation and releasedthereafter, reference may be had to the following: Carpenter Patent2,093,117 of September 14, 1937; Carpenter Patent 2,089,921 of August10, 1937; Williams et al. Patent 1,543,967, June 30, 1925; Moody et alPatent 2,161,376 of June 6, 1939; Carpenter Patent 2,235,803 of March18, 1941;

-and King et a1. Patent 2,236,246 of March 25,

For the manner in which the senders and markers cooperate to effectrepeated trials and to choose alternate routes when the direct routetrunks are busy, reference may be had to the Williams et al. Patent1,543,967 of June 30, 1925; Kerr Patent 1,577,033 of March 16, 1926; andto the Carpenter Patent 2,093,117, September 14, 11937 and the CarpenterPatent No. 2,235,803, above noted.

Although the signal sending and receiving equipment is illustratedherein as comprising an individual part of each sender, it will beunderstood that this equipment may be common to the senders in an ofliceand may be seized by any sender whenever it is needed to transmit orreceive signals.

The operators position equipment in the calling local office may be ofany suitable type,

equipped with a keyboard or with a dial for. setting the registersender.

The trunks interconnecting the several oifices:

sumed first that the subscriber of line 299. wishes.

to converse with the subscriber on line E3533. in a distant office.Referring to Fig. 1, it may also be assumed that the calling line 229belongs to the local ofiice 2M: served by the toll ofiice 480. Also, itmay be further assumed. that the called line I 383 belongs to a localofiice 83526 which is served by the terminating toll office. iiiifl. Itwill be noted, further that theoriginating and terminating toll ofiicesilifi and i238, respectively, and the four intermediate toll ofiicesM0,, 426, BOO-and 9m, disclosed in, the detailed drawings, correspond tothe toll omces illustrated in the routing diagram of Fig. 1.

The calling subscriber manipulates his dial 2 I0.

and-extendshis line over automatic switches.(not

7 shown), to theservice operators position in the local ofiice. Theoperator responds with. her cord circuit 2H, obtains the information concerning the desired subscribers office name and line number and proceedsto forward. the call by connecting her cord circuit 2H to an idle trunk28! extending to the district selector switch 202. Seizure of the trunk2% causes the trunk control mechanism 2P2 to function and: initiate theoperation of the sender connector The connector 2% connects the trunk2&5 to an idle register sender, and a visualsignal oradial tone issentto the operator. The operator verifies the calling subscribersnumber, if necessary, and then manipulates her dial or keyboardassociated with the position equipment 228' to. transmit designationsignals over the trunk Ziii through thesender connector to the selectedidle register sender. The signal or, impulse circuit over which these;designation signals are transmitted includes the tip and ringconductors-oi the trunk 20!, conductors H3 and 2M, conductors. Ziiand216; and a signal receiving relay 33.3, The first fivedigits representthe code of the terminating.

toll ofmce, and the impulsesrepresenting these digits are transmitted,by the relay, 333,111 the well-known manner to the fivesuccessive tollcode registers 3532 to 396, inclusive. The next seven digits representthe code of the local called ofiice and the number of the ,called line,and these digits are successively registered on the registers 30! to M3,inclusive.

At the proper time the registersender causes.

the operation of the marker connector 3E5, to connect the numerouscontrol conductors from the, sender to the marker. Thereuponthe tollcode digits are transferred from registers 332, to 306 over a pluralityof conductors, represented by the line 334, to the marker 3M. The markertransmits the toll code (translatedif necessary) to set the transmittingregisters 3 i 6'. The signals for setting the transmitting registers aresent;

from the marker back to the sender-over con-- ductors.335. The markeralso tests the group of trunks extending to the originating'tollofficeMill; selects an idle trunk 2&5 inthe group, and

operates the switches 2G2oand 2534- throughthe-- connectors 286. and20:7 to. extend the connection from; trunk Ziill and. over the trunk285. to the: toll office. The connection. havingthusbeenew tended to thetoll. office, a; signaling relay 33.55 is; operated to transmit, aseizure. signal to the toll oifice. Relay 336 connects: the channelfilter 3,315 and amplifier 338 to the winding of transformer: 3.39. Asignal current. of the selected frequency is thus transmitted from theharmonicgenerat-on 3H3 through the primary Winding of the transformer339. Current of thisv frequency is in.- duced in the secondary windingof the transformer and flows over the signal circuit. 3M1; through theconnector 2665, over signal circuit 2!], and thence over the extendedconnection. to the controlling equipment al sassociated with theincoming end of the trunk 2S5 in the toll oflice. signal causes theautomatic switch idzto extend the trunk 205 to the junctor Mid; and thejunc tor 4611 initiates the operation of: the sender connector 403toextend the junctor: through to an idle register sender in the toll.office.

Assoon as the toll offi'ce' sender is seized, it

transmits a signal-back to the sender in the calling local office tonotify thelatter sender that.

the toll code may be transferred to the tolloifi'oe. Thissignal' may betransmitted by operating the relay 5. Relay 5! I oonnectsthe harmonicgen-- erator M2 through the channel filter and amplifier 5i3 and 5M tothe primary-'windingof the transformer 5H5. The signal. currentgenerated in the secondary winding of the trans-- channel filter anddetector 326 andB'B'bto operate thesignal relay 34!. The operation ofrelay 3%! is a signal to thesender that the sender in the-originatingtoll office-is ready to receive the-tollcode, Thereupon the signaltransmitting channels 322 are rendered-effective b'y'the transmittingregisters and controlling circuit-s 3-16 toenergize the primarywinding-of transformer 353 with currents of frequencies representing thetranslated digits of the called tol-l' ofiicecode.

Signal currents of correspondingfrequencies: are induced inthetransmitting circuittfi and sent" overthe extended connection, to the,originating toll ofiice Wherethey are conducted? over'the circuitfill-through the normal contacts ofrelay 51-6 to the signal receiv-ingmechanism- 566. After.

passing the amplifier and after: being selected:

by thecorresponding channel filters 549, 520',

52!, they are detected and utilized to setthe toll" office registers l,562, 583,596 anditfi iniaccordance with the code; of the calledtolloffi'ce. At,

the same time, a signal is sent by the channel transmitting mechanism 3Min, the callinglocal' oificeto' notify the toll ofice 4G3 that. itis tobe the originatingtolloflice for this. particular call. This signal maybetransmitted by the. operationof relay 345', which. serves tovcomplete.

the signal channel including the filter 3%: At

the toll oifice the signal isireceivedjand;selected.

bythe channel filter 522'and. causes. the. opera? tion of relay 523.1The operation of relay 5233s, the signal to the tollpoflice sender. thatthe callis one that originated-inithis toll ofiice.

Following-the receipt of the toll code from the In any. Wfillr-kIIOWl'Imanner: the seizure local office, the marker connector 602 is operatedto connect the sender to the marker I. Thereupon the toll code istransferred from the registers 50! to 505, inclusive, over a group ofconductors 523 through the connector 002 and over conductors M3 to setthe corresponding registers 803 to 801 in the marker. The code isanalyzed by the marker and is sent back over conductors 814 andregistered on the transmitting registers 5I0 in the sender. The markeralso utilizes the toll code registration for selecting and operating aroute relay 810 representing the preferred route 401 outgoing from theoriginating toll office 400 in the direction of the terminating officeI200. In the well-known manner the route relay 0i0 causes the testing ofthe trunks in the preferred route, the selection of an idle trunktherein and the automatic operation of the switches 402 and 404 toextend the connection from the junctor 401 over the trunk 401 to thefirst intermediate toll office 410.

It is assumed that the trunk 401 is the preferred route trunk forextending calls from the toll office 400 to the toll office 1200 andthat trunks 409, 4H, 9H and 014 are the preferred routes, respectively,for toll offices 0, 420, 900 and 9I0. Therefore, no initial adjustmentis needed in the routing circuit (Figs. 6 and '7) of the originatingoffice 400;

Since the preferred route 401 is found idle and chosen as the first linkin the desired connection, a success signal is sent to the routingmechanism to register therein the fact that route 401 has been chosen.The success signal is effected by closing a circuit from the marker overconductor 815 through the connector 802, conductor 524, through thewinding of relay 525 to battery. Relay 525 operates and closes a circuitfrom the positive pole of battery through its armature and contact,contact of relay 521, conductor 526, back contact of polarized relay60!, back contact and winding of polarized relay 602 to ground. Thiscircuit is also extended through a back contact of relay 602 and theback contact and winding of relay 60! to ground. The polarity of therelays is such that only relay 602 responds and attracts its armatures.It may be noted at this point that the success and failure signals arerecorded in the route recording mechanism by the operation of polarizedrelays, the positive relays serving to register success signals and thenegative relays the failure signals. The polarity of these relays isindicated in the drawings by the positive and negative signs. When relay602 operates, it extends the circuit over conductor 526 through thefront contact of relay 602, conductor 603, contacts of relay 608,conductor 609, and thence to the next pair of polarized relays 604 and605.

This circuit 526, however, is held closed long enough to insure theoperation of relay 602 but not sumciently long to cause the operation ofthe relay 605 of the next pair. Relay 602, in operating, looks throughits front contact over a control conductor to the positive pole ofbattery. Thus, the operation of relay 602 extends the incoming circuit526 through to the circuit 603, this being an indication that the tollconnection has been extended successfully over the trunk 401 to the tollofiice M0. Had the preferred route 401 tested busy, the marker BI2 wouldhave closed a circuit over conductor 816, causing the operation of relay521. Relay 521 operating would close a circuit from the negative pole ofbattery over conductor 526 to the polarized relays 6M and 602. In thiscase, relay Bill contact of relay 608,

would operate, extending the circuit 526 to the polarized relays 606 and601 which serve to register the busy or idle condition of the alternateroute M6 extending from the toll ofiice 400.

In the manner already described, a seizure signal is transmitted by thesignal transmitting mechanism 529 in the originating oifice sender overthe trunk 401 to the toll office 4 l 0. The toll office 410 responds tothis signal and connects an idle sender to the trunk 401. The sender inthe office 4l0 transmits an acknowledgment signal, as above described,back over the connection to the sender in the office 400. Thereupon thetransmitting register 5!!! sends the toll code by means of signalingfrequencies selected by the filters 530, 53! and 532 through thetransformer 533 and over the extended connection to the registers of thesender in office 410.

The sender and marker in the ofiice 410 pro- 'ceed in the manner alreadydescribed to, extend the connection toward a succeeding ofiice. To thisend the marker in oflice M0 first tests the preferred route 409 for anidle trunk. If an idle trunk in this preferred route is found, theconnection is extended thereover to the toll ofiice 420. At the sametime, the sender in the office 410 transmits a success signal over thetrunk 401., to the receiving mechanism 506 in the sender at office 400.This success signal is of a frequency corresponding to the channelfilter 534, and relay 525 operates. The positive pole of battery isconnected to conductor 526, and the circuit may be traced through theback contact of relay 60I, front contact of relay 602, conductor 603,back conductor 600, thence through the back contacts and windings ofrelays 604 and 605 to ground. Relay 605 alone operates and locks in itsholding circuit, thus extending the route registering circuit toconductor 6H1. Thus, the route mechanism in office 4l0 has aregistration that the connection has been extended successfully overroutes 401 and 409 to the office 420. At the same time that the office4! transmits the success signal to ofiice 400, it establishes in its ownrouting mechanism, in the manner previously described, a registration tothe effect that the preferred outgoing route 409 has been tested andselected. This is accomplished by operating a relay in the routingmechzaizism at office 4l0, corresponding to the relay Next, the senderin the office 4|0 transmits the toll office code over the trunk 409 tothe seized sender in the oflice 420. Thereupon office 420 furtherextends the connection over the preferred route 411 and transmits asuccess signal back over the connection to the senders in office M0 andin office 400. It should be noted at this point that the markers in thesuccessive omces release as soon as they have performed theircontrolling functions, but the senders are held to receive and transmitthe necessary signals while the connection is being established. Thesuccess signal received in office 400 again operates relay 525 andapplies positive potential over conductor 526 to conductor 610. Thecircuit over conductor 6 I 0 may be further traced through the backcontacts of relay 608, back contacts of relay 6, thence through thecontacts of polarized relays (H2 and M3 to ground. Relay 6l3 aloneoperates in response to the success signal, looks through its holdingcircuit, and extends the route registering circuit over conductor M4 tothe next pair of registering relays H5 and M6. The success signal,however, is removed before relay 6H3 has

